I’ve been using the I2C RTC chip from STMicroelectronics, the M41T81, and I’ve managed to make a tiny little arduino library for it based on an existing library for the ubiquitous ds1307. I feel that it’s actually a better chip (on paper at least), it’s cheaper, does down to deciseconds and sets a bit when it has lost main power (so that you know when querying it).

I want to add very basic timezone support for it, since I’m dealing with UTC time internally for everything, and it’s nice to be able to read the time where you’re at. It’s going to be basic mainly because it will do dumb adds/subtracts, it won’t go into details of “is it the 28th of feb on a leap year?” which is enough for what I want.